This invention is directed generally to a novel and improved capacitive type proximity sensor, and more particularly to a novel combined protective housing and mounting apparatus for mounting a proximity sensor to a given surface.
While the present invention may be used in a variety of applications, the description will be facilitated by specific reference to the problem of monitoring the flow and level of feed material in a livestock feed delivery system. Modern livestock operations utilize extensive and often automated feeding systems for delivering feed to large numbers of livestock housed in confinement structures or buildings. Such feeding systems may be utilized in hog-raising operations as well as in chicken raising or laying operations, to deliver feed to the confined animals. Such feeding systems generally comprise one or more feed storage bins or hoppers which may be located exteriorly of one or more livestock buildings or confinement structures for holding a supply of feed for use over an extended period of time. Delivery of feed to the building or confinement structure may be by way of one or more tubular conduits, often with auger-like or other drive elements therein for advancing the feed. Once in the confinement structure, a series or system of similar, generally tubular auger conveyors delivers the feed to a system of individual feeding trays or pans, to continuous trough systems, or to other animal feeding apparatus. Generally speaking, portions of the conveyor systems are overhead, so as to deliver feed generally horizontally along or around the building, and then by gravity, through generally vertical drop tubes to the individual troughs, containers or the like. Moreover, additional intermediate hoppers, or metering devices may be utilized at some points in the system such as along the drop tubes intermediate the overhead delivery conduits and the troughs or individual feeding pans or the like.
Attempts have been made to monitor the flow and/or level of feed at various points in such a feed delivery system. For example, if a given point in the system should become clogged or overfilled, such that feed begins to back up in a drop tube or other part of the system, feed delivery should be shut off to all or part of the system until the conditions causing the backup are corrected. On the other hand, if feed fails to reach some part of the system, the absence of feed should similarly be detected an indicated to an operator so that appropriate corrective action may be taken.
We have attempted to sense the presence or absence of feed at various points in the delivery system by the use of capacitance or capacitive-type proximity sensors or switching devices. Generally speaking, such devices sense changes in the dielectric properties or capacitance of an area adjacent an electrode or sensor plate element thereof for switching between open circuit and closed circuit conditions. These open circuit and closed circuit conditions may readily be detected as corresponding changes in voltage or current in a connected monitoring circuit, and utilized to control upstream or downstream equipment, or to alert an operator, as desired.
However, we have found available sensors of this type to be lacking in reliability in the typical livestock operation environment. That is, we have found the performance of such sensors to be adversely affected by conditions of humidity, dirt and the like which are found in the typical livestock operation. For example, the temperature and humidity often varies greatly between the outside bins or hoppers and the more controlled temperature and humidity conditions inside the livestock buildings. Especially during cold weather, the cold feed conveyed into the building from the outside bins causes considerable condensation on the external surfaces of the delivery conduits and related equipment as it pases therethrough. In an animal-filled barn, it will be appreciated that the temperature and humidity levels will be relatively elevated. Hence, relatively cold feed delivered from outside quickly cools the delivery equipment below the dew point and moisture condenses onto the equipment, often to the point of being literally "dripping wet".
Moreover, the feed itself may vary greatly in its moisture content, due to inherent variations in the moisture content of various feeds, as well as the storage conditions and the weather conditions as discussed above. It should be appreciated that such variations in moisture conditions and/or content effect the dielectric properties of the feed. This in turn effects the performance of the capacitive-type sensor which is intended to operate based upon sensed changes in dielectric properties of an adjacent electrical field to sense the presence or absence of feed.
Such variation of the dielectric properties of the feed may greatly diminish the reliability of the desired switching operation of such a sensor. For example, in the case of sensing the backup of feed in a drop tube, it will be appreciated that the sensor must not switch or change conditions while the feed is moving or falling in the drop tube. However, when the feed backs up in the drop tube due to filling or blockage of downstream equipment, the switch must then reliably trigger or change conditions to either give an appropriate signal to an operator or directly operate appropriate upstream equipment for corrective action. Hence, sensitivity of such a capacitive-type switch or sensor to environmental conditions can greatly decrease the desired reliability of operation thereof, given the relatively limited range of dielectric variation over which operation is desired in such applications.